This application is based on Japanese Patent Application HEI 11-231998 filed on Aug. 18, 1999, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a solid-state image pickup device, and in particular, to a structure of a vertical charge transfer path of a solid-state image pickup device.
b) Description of the Related Art
FIG. 9 generally shows a solid-state image pickup device in a plan view.
The configuration of FIG. 9 includes a solid-state image pickup device 100 including a semiconductor substrate 101 and a large number of pixels 103 arranged in a matrix (i.e., in rows and columns). Each pixel 103 includes a photodiode (a photoelectric converter or transducer element) 103a, a readout gate or a transfer gate 103b. 
For each column of pixels, a vertical charge transfer path 105 is formed. Each path 105 includes a layer of a semiconductor of first conductivity type (n-type). The readout gate 103b is disposed between each photodiode 103a and the first-conductivity-type semiconductor layer. The first-conductivity-type (n-type) semiconductor layer is used as a charge transfer channel. The configuration further includes a horizontal charge transfer path 107 and an amplifier 111.
Each vertical charge transfer path 105 includes an end electrically connected to the horizontal charge transfer path 107. The horizontal path 107 includes an end connected to the amplifier 111.
The photodiode 103a generates an electric signal (electric charge) through photoelectric conversion. The signal or charge is transferred via the readout gate 103b to the vertical charge transfer path 105. The charge is vertically transferred through the path 105, for example, by four-phase driving and is delivered to the horizontal charge transfer path 107. In the path 107, the charge is transferred to the amplifier 111, for example, by two-phase driving. The amplifier 111 amplifies the electric signal thus transferred and outputs information of an image to an external device.
The solid-state image pickup device 100 includes a field area or zone 117 other than the areas in which the constituent components such as the photodiodes 103a, the readout gates 103b, the vertical charge transfer paths 105, the horizontal charge transfer paths 107, and the output amplifier 111 are disposed.
In this structure, it is desirable to prevent surmounting of electrons over, for example, areas (1) to (3), listed below, in the field area 117. This is because the surmounting of electrons possibly causes an erroneous operation in the image pickup device 100.
(1) An area other than the readout gate 103b in an area between the photodiode 103a and the associated vertical charge transfer path 105 (first areas 121a and 121b of FIG. 9).
(2) An area between the vertical charge transfer path 105 and the photodiode 103a which is not connected by the readout gate 103b to the path 105 and which is horizontally next to the path 105 (a second are 125 of FIG. 9).
(3) An area between vertically adjacent photodiodes 103a among the photodiodes 103a connected via the readout gate 103b to the vertical charge transfer path 105 (a third area 131 of FIG. 9).
To prevent the erroneous operation above, there is formed, in a periphery of the first-conductivity-type (n-type) semiconductor layer of each vertical charge transfer path 105 in a plan view, an isolation area rib or zone such as a channel stop area in other than the areas in which the readout gates 103b are arranged. Similarly, between the photodiodes 103a sequentially arranged in a direction of the pixel column, an isolation area such as a channel stop area is disposed.
When the image pickup devices 100 has a pixel density not exceeding a particularly large value, distance between the photodiodes 103a in the first to third areas 121, 125, and 131 or distance between the photodiodes 103a and the vertical charge transfer path 105 therein can be set to a fully great value. Namely, the isolation areas having a sufficient width can be manufactured in these areas 121, 125, and 131. Consequently, there exists little fear of the erroneous operation above.
However, with increase in the pixel density of solid-state image pickup devices in recent years, it is difficult to take such satisfactorily long distance, for example, between the photodiodes 103a or between the photodiodes 103a and the vertical charge transfer path 105 in the first to third areas 121, 125, and 131. The isolation area cannot have sufficient width in the areas 121, 125, and 131.
In a case in which the isolation area is formed by a channel stop area, the electric isolation can be desirably obtained by increasing an impurity concentration of the channel stop area even if width thereof is reduced to a relatively narrow value.
However, when the impurity concentration is increased in the channel stop area, narrow channel effect easily occurs in a place where the channel stop area is disposed on both sides in a direction of width of the first-conductivity-type (n-type) semiconductor layer of the vertical charge transfer path. The narrow channel effect then locally changes a transfer efficiency and a saturation output of charge in the vertical charge transfer path. It is therefore difficult to transfer charge to the horizontal charge transfer path in a stable state.
Particularly, the narrow channel effect easily appears in a solid-state image pickup device including a shifted-pixel layout, which no expected as a structure to cope with high pixel density.
It is therefore an object of the present invention to provide a solid-state image pickup device capable of solving the problem associated with increase in the pixel density.
According to one aspect of the present invention, there is provided a solid-state image pickup device, comprising: a semiconductor substrate having a two-dimensional surface; a large number of photoelectric converter elements including a semiconductor region of first conductivity type, said photoelectric converter elements being arranged on the surface of said semiconductor substrate in a plurality of columns with a fixed pitch and a plurality of rows with a fixed pitch, said photoelectric converter elements in each odd column being shifted about one half of the pitch in each said column relative to said photoelectric converter elements in each even column, said photoelectric converter elements in each odd row being shifted about one half of the pitch in each said row relative to said photoelectric converter elements in each even row, each said photoelectric converter element column including said photoelectric converter elements of only said odd rows or said even rows; a plurality of isolation areas each formed on the surface of said semiconductor substrate between each pair of adjacent ones of said photoelectric converter element columns, each said isolation area including a semiconductor layer of second conductivity type generally extending in a direction of said photoelectric converter element column, while locally meandering; and a plurality of vertical charge transfer paths each formed between each said photoelectric converter element column and adjacent one of said isolation areas on one side of said photoelectric converter element column in a direction of said photoelectric converter element row, each said vertical charge transfer path including a semiconductor layer of first conductivity type generally extending in said photoelectric converter element column direction, while locally meandering, said vertical charge transfer path having width W1 between each said photoelectric converter element of said column and said adjacent isolation area and width W2 between said photoelectric converter elements adjacent to each other in said column, said width W2 being larger than said width W1.
According to another aspect of the present invention, there is provided a solid-state image pickup device, comprising: a semiconductor substrate having a two-dimensional surface; a large number of photoelectric converter elements arranged on the surface of said semiconductor substrate in a plurality of columns with a first pitch and a plurality of rows with a second pitch, said photoelectric converter elements in each odd column being shifted about one half of the second pitch relative to said photoelectric converter elements in each even column, said photoelectric converter elements in each odd row being shifted about one half of the first pitch relative to said photoelectric converter elements in each even row, each said photoelectric converter element column including said photoelectric converter elements of only said odd rows or said even rows; an isolation area formed on said semiconductor substrate on a predetermined first side of each associated photoelectric converter element column, said isolation area generally extending, while locally meandering, in a direction of said photoelectric converter element column; and a vertical charge transfer path including a semiconductor layer of first conductivity type formed on said semiconductor substrate on a second side of each associated photoelectric converter element column, the second side being opposite to the first side, said semiconductor layer generally extending, while locally meandering, in a direction of said photoelectric converter element column, and being contiguous, in every regions between adjacent two of said photoelectric converter elements in said associated photoelectric converter element column, to said isolation area for the associated column while being contiguous to another said isolation area for the column next to the associated column on the second side, said semiconductor layer having width W1 in a section in which said semiconductor layer is contiguous only to said another isolation area on the second side and width W2 in a section in which said semiconductor layer is contiguous to said isolation area on the first side and said another isolation area on the second side, said width W2 being larger than said width W1.
By selecting the width of the first-conductivity-type (n-type) semiconductor layer constituting the vertical charge transfer path as up above, the disadvantageous event in which the narrow channel effect locally changes the transfer efficiency and the saturation output of charge in the vertical charge transfer path can be suppressed.
The width (to be referred to as an xe2x80x9ceffective vertical charge transfer path widthxe2x80x9d in this specification) of the area which can function, when an operating voltage is applied to the solid-state image pickup device, as an actual charge transfer path in each vertical charge transfer path can be substantially kept a constant value in a plan view. Electric charge can be accordingly transferred by each vertical charge transfer path in a stable state.